Anterior cruciate ligament (ACL) injuries are a significant problem for athletes, and women in particular. Both surgical and non-surgical treatment options exist, with the ultimate goal of regaining joint stability, knee kinematics, and quadriceps strength compared to the uninjured contralateral limb to allow full return of function and activity level and to prevent additional injury to the cartilage and the meniscus in the knee which might lead to an increased likelihood of osteoarthritis (OA). Published research has demonstrated clinically relevant effects of perturbation of support surface training for both ACL-deficient and ACL-reconstructed populations for improving dynamic knee stability, particularly in females. The clinically available methods of delivering the desired perturbations are currently limited to static balance boards that are manually pushed or pulled by the physical therapist. These perturbations may not simulate real-life perturbations that would occur during walking or running. The Principal Objective of this Fast Track SBIR project is to develop and validate a cost-effective commercial product, ActiveStep-Sport", for providing task-specific, neuromuscular, dynamic perturbation training to improve outcomes for both conservative and surgical treatment of ACL injury (ACL), particularly in young athletes and women. PUBLIC HEALTH RELEVANCE: The proposed ActiveStep-Sport system provides the enabling technology for large-scale application of clinically relevant perturbation of support surface training for anterior cruciate ligament (ACL) injury rehablitiation. Approximately 100,000-175,000 ACL reconstructions performed annually in the US annually, with females significantly more likely to suffer an ACL rupture than males. Perturbation training in certain ACL injured populations has been shown to reduce episodes of giving way and to reduce abnormal knee kinematics, both of which often lead to an inability to regain functional levels of sports participation and increase the potential for developing knee osteoarthritis. Use of perturbation training is hypothesized to improve knee kinematics compared to strengthening alone, and to improve outcomes for ACL rehabilitation. The technology developed here represents a translation of validated laboratory-based research methodology to a system more suited for widespread clinical use. If technically and economically feasible, ActiveStep-Sport will help reduce the overall health care costs associated with the treatment and rehabilitation of ACL injuries and the onset of osteoarthritis.